Add another entry to the lengthening list of reduced revenue estimates for Facebook.

eMarketer said in a report issued earlier today that it has cut its 2012 revenue estimates on Facebook from more than $6 billion to around $5 billion.

In February, eMarketer estimated that Facebook's total revenues would go beyond the $6 billion mark this year, but the company's underwhelming performance in the first and second quarters of 2012 has changed the opinion of analysts.

The new estimate has Facebook's revenue at a 35.9 percent increase from 2011, according to eMarketer's forecast, but analyst expects that percentage to grow when Facebook establishes its ad exchange, and its mobile ad business.

While advertising numbers are still rising -- eMarkerter expects revenue to hit $4.23 billion, a 34.1 percent increase from 2011 -- the climb is not as significant as last year. Revenue from Facebook payments and other sources, however, are increasing quickly. This year Facebook will see $811 million from non-advertising services -- a 45.6 percent increase from last year.

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